Unable to see or update a review which has been created/assigned/commented by a deleted user

2011.12.16 14:08:54 ERROR o.s.s.ui.JRubyFacade  Fail to render: http://foo.com/reviews?statuses%5B%5D=&severities%5B%5D=&projects%5B%5D=4711&author_login=&assignee_login=bar&false_positives=without&review_id=&sort=&asc=false&commit=Search
undefined method `user' for nil:NilClass
        On line #152 of app/views/reviews/index.html.erb

    149: <%= link_to h(review.title), :controller => "reviews", :action => "view", :id => review.id -%>
    150: <div class="comment-excerpt">
    151: <img src="<%= ApplicationController.root_context -%>/images/reviews/comment.png"/>
    152: &nbsp;<b><%= comment.user.name -%> :</b>
    153: <%= comment.excerpt -%>
    154: </div>
    155: </td>

    app/views/reviews/index.html.erb:152
    org/jruby/RubyArray.java:1602:in `each'
    app/views/reviews/index.html.erb:139
    org/jruby/RubyKernel.java:2056:in `send'
    org/jruby/RubyKernel.java:2064:in `send'
    org/jruby/RubyProc.java:268:in `call'
    org/jruby/RubyProc.java:228:in `call'
    file:lib/jruby-rack-1.0.0.1.jar!/vendor/rack-1.2.1/rack/head.rb:9:in `call'
    file:lib/jruby-rack-1.0.0.1.jar!/vendor/rack-1.2.1/rack/methodoverride.rb:24:in `call'
    file:lib/jruby-rack-1.0.0.1.jar!/rack/adapter/rails.rb:36:in `serve_rails'
    file:lib/jruby-rack-1.0.0.1.jar!/rack/adapter/rails.rb:41:in `call'
    file:lib/jruby-rack-1.0.0.1.jar!/jruby/rack/rails.rb:185:in `call'
    file:lib/jruby-rack-1.0.0.1.jar!/rack/handler/servlet.rb:19:in `call'